We found a lake in Colorado! Lake Horsetooth is in Fort Collins, and such a nice lake. Doesn't quite have the beaches like MN, but we'll take it! It's only 2 hours away and not way back into the mountains. We took a day trip to downtown Fort Collins and had a great time eating new food (Afghanistan food - surprisingly very good!), walking the quaint town and spending the afternoon at the beach.
Here's some pictures!
The water looks dirty, but it's actually crystal clear! Near the shore, the red dirt gets churned up.